1. Field of the Invention
This invention relates to a power transmission apparatus having a torque limiter function, or in particular a power transmission apparatus suitably applicable to a compressor of an automotive air conditioning system operated through a belt or the like from an external power source such as an engine.
2. Description of the Related Art
FIG. 6 is a longitudinal sectional view of a power transmission apparatus for transmitting power to a compressor from an engine or motor, described in Japanese Patent Application No. 2005-304627 filed by the present applicant. The power transmission apparatus of this type, as shown, includes a pulley 100 constituting a driving-side rotary member for acquiring driving power from the engine or the like, a power shutoff member 300 constituting a torque limiter and hub 200 constituting a driven-side rotary member fixed to a rotary shaft 400 of the compressor. Pulley 100 is supported rotatably on a casing 700 of the compressor through a bearing 500, and hub 200 is coupled by being inserted into pulley 100. Power shutoff member 300 is provided for preventing secondary problems, such as breakage of a belt due to excessive torque which may be generated by, for example, the seizing of the compressor, and has a breakable portion 301 to disconnect by breaking the power transmission path at the time of an excessive torque generation.
The power transmission apparatus of this type is normally required to have the torque damper function for decreasing an abrupt change in transmission torque, and for this purpose, includes a hub-side protrusion 201 formed of an elastic material such as rubber arranged on the hub side. Hub 200 and pulley 100 are coupled to each other by fitting hub-side protrusion 201 and the depression formed on pulley 100 with each other, so that torque is transmitted through the protrusion and the depression.
In the case where excessive torque is generated in the power transmission apparatus having this structure, power shutoff member 300 is activated and breaks the breakable portion. After power shutoff member 300 breaks, pulley 100 and hub 200 are simply in a state with the protrusion inserted in the depression, and therefore hub 200 easily comes off from pulley 100.
For this reason, an anti-separation means has been proposed for the power transmission apparatus shown in FIG. 6. This anti-separation means is composed of a hook-shaped protrusion 205 projected axially from the rear end surface of hub-side convexo-concave portion 201 of hub 200 and an insertion hole 105 on the side of pulley 100 into which the protrusion is inserted and engaged. In this case, protrusion 205 is inserted into and through insertion hole 105 to assure axial engagement. However, this anti-separation means, has a problem that the die is complicated in order to form the hook-shaped protrusion for an increased die cost. Another problem is that the rotary shaft portion of the protrusion 205 is comparatively small in diameter and therefore easily compressed and deformed in the axial direction by the resistance against the insertion of protrusion 205 into insertion hole 105, with the result that protrusion 205 cannot be easily pushed into an engageable position and the assembly time is lengthened.